1. Field
The present disclosure relates to a method and a system for color calibration and color profiling of an image output device, such as an image printing device.
2. Description of Related Art
Some image printing devices have inline color measurement equipment, such as an inline spectrophotometer (ILS), to perform color management functions (e.g., color profiling and color calibration). On the other hand, some image printing devices have a full width array (FWA) or partial width array (PWA) scan bar to evaluate and/or correct image quality variation in the cross-process direction of the image printing device.
The ILS is used for color management. While the ILS contributes significantly to better performance (i.e., productivity and customer convenience), the ILS measures the color (e.g., in a device independent color space, such as L*a*b*) at only one location in a cross-process direction of the image printing device, unless more than one ILS is used, which is more expensive. Consequently, when using a single ILS, only a few color patches can be measured on a page (e.g., 11 patches on a letter-size page). Since hundreds, or even thousands, of color patches are needed for color management functions, such as generating a destination profile for the printer or populating a spot color table, hundreds of pages are wasted each time such color management functions are updated. Moreover, the ILS cannot perform important uniformity measurements, such as IBOB (inboard-outboard) color variation. The inboard-outboard color variation in the print quality may be due to several factors, such as pressure variation across the length of the transfer nip.
Some image printing devices use an inline full-width array (FWA) scan bar for color management instead of the ILS. The FWA measures an image at all locations in the cross-process direction, and at high resolution (e.g., 600 dpi). The FWA measures many hundreds of patches on a page. However, the FWA typically provides only three channel (RGB) information at each pixel, instead of the reflectance spectrum (e.g., 31 wavelengths from 400 nm to 700 nm) provided by the ILS. It is possible to profile a scanner, such as a FWA scan bar, to generate color (L*a*b*) data from the RGB signals, but with available technology this can only be done approximately. The accuracy attainable is quite inadequate for some color management functions, such as generating a destination profile for the printer or populating a spot color table.
Therefore, it is desirable to have a system that provides color measurements that are sufficiently accurate for color management functions (i.e., like the ILS) and provides color measurements at many locations in the cross-process direction (i.e., like the FWA) to enable color management or calibration in fewer pages. It is also desirable for such system to perform color uniformity measurements accurately.
The present disclosure provides improvements in methods and systems for color calibration and color profiling of the image output devices.